A process of forming a thin film such as a silicon oxide film or the like on a substrate by supplying a precursor gas containing silicon or other element(s), an oxidizing gas and so on to the substrate may be performed during manufacture of semiconductor devices. In this case, the film can be formed at a relatively low temperature, for example by using a catalyst gas, thereby improving thermal history of the semiconductor devices.
When the above-mentioned film is formed on the substrate, a resistance to wet etching by hydrofluoric acid (HF aqueous solution) or the like can be improved by adding an element such as carbon or the like to the film.
However, under a relatively low temperature condition, a sufficient amount of carbon may not be introduced into the film, which may result in difficulty in obtaining a film having a high etching resistance. In addition, a film added with carbon may have a low ashing resistance.